Deep Dehydrogenation Research Articles

Tuning the Active Oxygen Species of Two-Dimensional Borophene Oxide toward Advanced Metal-Free Catalysis.

Two-dimensional (2D) borophene materials are predicted to be ideal catalytic materials due to their structural analogy to graphene. However, the lack of chemical functionalization of borophene hinders its practical application in catalysis. Herein, we reported a massive production of freestanding few-layer 2D borophene oxide (BO) sheets with tunable active oxygen species by a moderate oxidation-assisted exfoliation method. State-of-the-art characterizations demonstrated the evolution of active oxygen species from surface B-O species at the initial stage to the intermediate BxOy (1.5 < x/y < 3) species and eventually to bulk B2O3 with an increasing oxidation duration. As a result, the 2D BO sheet with enhanced B-O species exhibited a strikingly high catalytic activity for the aerobic oxidation of benzylamine into N-benzylidenebenzylamine. The formation rate of imine reaches as high as 29.7 mmol gcatal-1 h-1 under mild reaction conditions, higher than that of pristine borophene, boron oxides, graphene oxide, and other metal/metal-free catalysts in the reported literature. Density functional theory calculations further revealed the critical role of surface B-O species, which favor the adsorption and N-H activation of benzylamine for high activity and suppress the deep dehydrogenation, yielding an outstanding imine selectivity (>90%). This work paves the route for a moderate and scalable synthesis of few-layer BO sheets with highly active B-O species toward advanced metal-free catalysis beyond graphene.

Vitreous silica supported metal catalysts for direct non-oxidative methane coupling

Direct non-oxidative methane coupling (NMC) transforms methane into valuable chemicals and hydrogen, which is a promising pathway to boost industrial decarbonization. The reaction, however, is challenged by high C-H bond activation temperature, catalyst coking, and low selectivity towards hydrocarbon products. Here we studied the efficacy of five vitreous silica supported 3d transition metal (Mn, Fe, Co, Ni, and Cu) catalysts (denoted as M/SiO2-v) for NMC. These catalysts were prepared by flame fusion of mixtures of quartz and metal silicate precursors. The metal species in the as-synthesized catalysts were fully or partially oxidized, with their stability following the order of Mn > Fe ≈ Co > Ni > Cu in the NMC reaction. The Cu species has low methane reaction rate, due to the high adsorption and dissociation energies of methane. The Mn and Ni species have high methane reaction and coke formation rates, which is supported by easy kinetics of methane deep dehydrogenation to carbon. In contrast, Fe and Co species showed the best hydrocarbon product selectivity. Particularly, the Co species emerged as the optimal catalyst for NMC, showcasing a balanced methane activation, hydrocarbon formation, and low coke yield. The relationship between the evolved metal species under reaction conditions and their NMC performance was discussed. The present study screens and provides effective catalyst formulations for NMC reactions.

The types of metal M and crystal surface in the PtM (M = Co, Ni, Zn) IMCs catalysts to regulate catalytic performance of ethane direct dehydrogenation

PtM IMCs have improved catalytic performance of ethane dehydrogenation (EDH), however, identifying the functions of the types of metal M and crystal surface for the PtM IMCs catalysts in regulating EDH catalytic performance are still a challenge in experiment. This work fully investigated catalytic performance of EDH over three crystal surfaces (110), (111) and (200) of PtM IMCs (M = Co, Ni, Zn) by using density functional theory (DFT) calculations and kinetic Monte Carlo (kMC) simulations. The results show that the catalytic performance of EDH over PtM IMCs strongly depend on the types of metal M and crystal surfaces, the PtZn(111) catalyst is screened out as the most promising in EDH reaction with the optimal reaction temperature of 773.15 K. The geometrically isolated Pt site in the [PtM3] assembly of PtZn(111) could catalyze the CH cleavage, and C2H4* exhibits weak π-adsorption model at the individual Pt sites, promoting C2H4* desorption. Compared to (110) and (200) surfaces, the (111) surface with moderate Bader charge transfer showed the highest C2H4(g) production activity, and Zn atoms transferred more electrons to Pt atoms, which greatly weakened the charge transfer between C2H4* and the catalyst surface, favoring C2H4* desorption to inhibit C2H4* deep dehydrogenation. Moreover, the catalytic performance of PtZn(111) catalyst is superior to the industrially used PtSn catalyst. This work provides valuable structure clue for the design of high-performance catalyst in alkane direct dehydrogenation.

Unraveling the function of monolayer shell structure over Pt-based alloy catalysts in tuning ethane dehydrogenation reactivity and coking resistance

Ethane direct dehydrogenation (EDH) operated at high temperature easily leads to coke formation. The new core–shell catalysts with monolayer shell exhibited better catalytic performance, and the function of monolayer shell structure is of great importance. This work fully investigated catalytic performance of EDH over six types of core–shell Pt3M@Pt and Pt@Pt3M (M = Fe, Co, and Ni) catalysts with Pt3M and Pt monolayer shell under the experimental conditions. Here, density functional theory (DFT) calculations with kinetic Monte Carlo (kMC) simulations were employed. The results show that the metal M over Pt3M@Pt surface decreases coordination number of Pt-Pt and restricts deep dehydrogenation reactions. The Pt3M@Pt catalysts with d-band center close to Fermi level exhibit higher C2H4(g) formation activity than Pt@Pt3M catalysts at 873.15 K. H2(g) co-feeding significantly decreases the coverage of coking C*+CC* species. The screened Pt3Ni@Pt catalyst presents the highest C2H4(g) formation activity and 100 % selectivity at the H2(g) partial pressure of 0.1 bar and reaction temperature 873.15 K, which is superior to previously reported Pt, Pt3Sn, 1Pt3Sn@4Pt, Pd1-NDG, Pt2/Al2O3 and Rh/ZrO2 catalysts. H* adsorption energy is proposed as a descriptor to quickly evaluate C2H4(g) formation activity. This work provides a useful strategy for designing alkane dehydrogenation catalysts by tuning monolayer shell structure and coordination environment of active site.

Propane dehydrogenation over Pd-Bi intermetallic compounds: A DFT combined with microkinetic modeling study

Propylene is an important industrial raw material. The high temperature needed by the propane dehydrogenation (PDH) on the pure Pt or Pd catalyst may give rise to hydrogenolysis and carbon deposition, which ultimately poisons the catalysts. Experiments synthesized a series of Pd-Bi intermetallic compounds loaded on SiO2. The Pd-Bi/SiO2 catalyst with a moderate Bi concentration bears high activity and selectivity. But the reason is unknown. In the present paper, the DFT calculation and microkinetic modeling were performed to study the reaction network of PDH on the Pd(100), Pd3Bi1(100), Pd2Bi1(100), Pd1Bi1(100), Pd(210), and Pd1Bi1(210). Due to the isolated Pd sites, Pd1Bi1(100) and Pd1Bi1(210) showed the highest propylene selectivity but low TOF of propylene. The Pd2Bi1(100) may be more suitable for PDH because of the compensation between activity and selectivity. Two selectivity descriptors (ΔEselec,1 and ΔEselec, 2) could measure the influence of deep dehydrogenation and hydrogenolysis on the selectivity for propylene in the PDH, respectively. The barriers for both C-C crack and propylene deep dehydrogenation approximately increase with Bi concentration, which may be why both ΔEselec,1 and ΔEselec, 2 succeed in predicting the propylene selectivity on the pure Pd and Pd-Bi catalysts.

Oxygen Vacancies Alter Methanol Oxidation Pathways on NiOOH.

A thorough comprehension of the mechanism underlying the methanol oxidation reaction (MOR) on Ni-based catalysts is critical for future electrocatalytic design and development. However, the mechanism of MOR on these materials remains a matter of controversy. Herein, we combine in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations to identify the active sites and determine the mechanism of MOR on monometallic Ni-based catalysts in alkaline media. The SEIRAS results show that formate and (bi)carbonate are formed after the commencement of the MOR with potential-dependent relative distributions. These spectroscopic results are in good agreement with the DFT-computed reaction profiles over an oxygen vacancy, suggesting that the MOR mainly proceeds through the formate-involving pathway, in which the early consumption of methanol yields formate as the major product, while increasing potential drives further oxidation of formate to (bi)carbonate. We also find a parallel pathway for the generation of (bi)carbonate at high potentials that bypasses the formation of formate. The two main pathways are thermodynamically more feasible than the one predominantly reported in the literature for MOR on NiOOH that involves CHO and/or CO as key intermediates. These DFT results are supported by spectroscopic evidence showing that no band associated with CHO or CO can be detected by SEIRAS, which is attributed to the nature of the oxygen vacancies as the active sites, suppressing deep dehydrogenation of CH2O to CHO. This work thus shows the promising role of defect engineering in promoting the electrocatalytic MOR activity and selectivity.

Regulating metal-acid double site balance on mesoporous SiO2-Al2O3 composite oxide for supercritical n-decane cracking

The balance between metal and acid sites directly affects the preparation of high-performance cracking catalysts with high heat sink and low coking. Nevertheless, how to control acid-metal sites balance and its relationship with cracking performance are reported scarcely. In this work, a series of Pt/Al2O3-SiO2 dual sites catalysts with different metal to acid active sites ratio (CM/CSA) were constructed by ethanol-assisted impregnation method and the impact on n-decane cracking under supercritical conditions was systematically and deeply investigated. The results showed that the conversion and carbon deposition increased gradually with varied CM/CSA and reached the balance at CM/CSA of 0.13. The proper ratio CM/CSA (0.13) can balance the deep dehydrogenation coking over metal active sites and high heat sink of cracking over acid active sites, the chemical heat sink reaches amazing 1.75 MJ/kg and carbon deposition is only 22.03 mg/cm2 at 750 °C. Meanwhile, the few metal sites at low CM/CSA and the few strong acid sites at high CM/CSA are the main factors limiting the cracking activity. Low CM/CSA limit the activation of C–H bond and deep dehydrogenation of coking precursor, resulting in relative low cracking activity and carbon deposition, while high CM/CSA limit the activation of C–C bond and increase the deep dehydrogenation. In this contribution, design and construction of metal-acid dual sites can not only provide the technical solution for the preparation of high heat sink and low coking cracking catalyst, but also deepen the understanding of the cracking path of hydrocarbon fuel.

Alkaline-earth ion stabilized sub-nano-platinum tin clusters for propane dehydrogenation.

The strong promotion effects of alkali/alkaline earth metals are frequently reported for heterogeneous catalytic processes such as propane dehydrogenation (PDH), but their functioning principles remain elusive. This paper describes the effect of the addition of calcium (Ca) on reducing the deactivation rate of platinum-tin (Pt-Sn) catalyzed PDH from 0.04 h-1 to 0.0098 h-1 at 873 K under a WHSV of 16.5 h-1 of propane. The Pt-Sn-Ca catalyst shows a high propylene selectivity of >96% with a propylene production rate of 41 molC3H6 (gPt h)-1 and ∼1% activity loss after regeneration. The combination of characterization and DFT simulations reveals that Ca acts as a structural promoter favoring the transition of Snn+ in the parent catalyst to Sn0 during reduction, and the latter is an electron donor that increases the electron density of Pt. This greatly suppresses coke formation from deep dehydrogenation. Moreover, it was found that Ca promotes the formation of a highly reactive and sintering-resistant sub-nano Pt-Sn alloy with a diameter of approximately 0.8 nm. These lead to high activity and selectivity for the Pt-Sn-Ca catalyst for PDH.

Activation of Cr2O3 for propane dehydrogenation by doping with Pt single-atom promotor

In this work, we evaluate reaction mechanism and kinetics of propane dehydrogenation (PDH) over Pt single-atom-doped Cr2O3 catalyst by combining density functional theory calculations and microkinetic analysis. Pt single-atom-doped Cr2O3 achieves superior propane conversion and propene selectivity to PtSn alloy and pristine Cr2O3 under typical operating conditions. Pt serves as a promoter to activate nearby Cr-O Lewis-Pair sites. The promotion effect of Pt single-atom on activity is attributed to the lowered energy level of conduction band minimum of nearby O Lewis-base site, enhancing its H capture ability and accordingly facilitating first step of dehydrogenation of propane. The Pt single-atom promoter also enhances propene selectivity by adjusting the Cr-O Lewis acid-base interaction with the deep dehydrogenation product, impeding deep dehydrogenation process. This work provides theoretical insights into the feasibility of atom-level dispersion Pt promoter activating CrOx-based catalysts for PDH process, and guidance for future rational design of other oxide-supported single-atom catalysts for PDH.

Zeolite fixed cobalt–nickel nanoparticles for coking and sintering resistance in dry reforming of methane

Dry reforming of methane (DRM) displays a crucial role in CO2 fixation, but the current catalysts suffer from deactivation from thermodynamically oriented coking and metal sintering. Herein, we reported a catalyst by fixing the cobalt–nickel nanoparticles within the zeolite crystals (CoNi@zeolite), where the SiOx-O-Mδ+ (M = Ni or Co) linkage enhanced the reduction resistance of Co and Ni species compared with the generally supported catalysts, efficiently hindering the deep dehydrogenation of methane, which is well known as a reaction channel for coke formation. In addition, the rigid and thermally stable zeolite framework stabilized the cobalt–nickel nanoparticles to avoid their sintering during the reaction. As a result, the CoNi@zeolite catalyst exhibited a long reaction lifetime and great regenerability in a test for 980 h with reaction gas flow at 1200 L per unit mass of metal species per hour, outperforming conventionally supported metal catalysts. This work enables a proof-of-the-concept design of durable catalysts by zeolite fixation for the reactions in strongly reductive atmospheres.

Density functional theory study on direct dehydrogenation of propane catalyzed by N-, O-, and P-doped graphene catalysts

The density functional theory was used to calculate the reaction mechanism and selectivity of nonmetallic single-atom catalysts, such as N, O, and P, doped on graphene in the direct dehydrogenation of propane (PDH) . Our results show that the rate-controlling step in PDH varies with the doping atom. We also found that N, O, and P nonmetallic single-atom-doped graphene catalysts showed relatively low adsorption performance for propane and the active site was the C atom adjacent to N, O, and P, rather than the doped atom itself. Interestingly, for the O-doped graphene catalysts, which can reduce the reaction energy barrier by searching for multiple transition states, and the more transition states in the reaction path, the lower the energy barrier for the reaction rate-controlling step. Finally, the results show that the energy barrier of P-doped propane direct dehydrogenation reflecting the speed control step is the lowest, which is 44.32 kcal·mol−1, and the energy barrier of deep dehydrogenation is 53.08 kcal·mol−1; so it has good selectivity. Therefore, the P-doped graphene catalyst has a promising application as a nonmetallic catalyst for the direct PDH, which provides the possibility for the design of cheap and environmentally friendly catalysts.

Remarkable N2-selectivity enhancement of NH3-SCR over HPMo modified MnCo-BTC@SiO2 catalyst

In this work, the phosphomolybdate (HPMo) modification strategy was applied to improve the N2 selectivity of MnCo-BTC@SiO2 catalyst for the selective catalytic reduction of NOx, and further, the mechanism of HPMo modification on enhanced catalytic performance was explored. Among MnCo-BTC@SiO2-x catalysts with different HPMo concentrations, MnCo-BTC@SiO2-0.75 catalyst exhibited not only the highest NH3-SCR performance (∼95% at 200-300°C) but also the best N2 selectivity (exceed 80% at 100-300°C) due to the appropriate redox capacity, greater surface acidity. X-ray photoelectron spectrometer (XPS) and temperature programmed reduction of H2 (H2-TPR) results showed that the modification with HPMo reduced the oxidation-reduction performance of the catalyst due to electron transfer from Mo5+ to Mn4+/Mn3+ and prevent the excessive oxidation of ammonia adsorption species. NH3 temperature-programmed desorption of (NH3-TPD) results showed that the modification with HPMo could significantly improve the surface acidity and NH3 adsorption, which enhance the catalytic activity and N2 selectivity. In-situ diffused reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) revealed that modification with HPMo increased significantly the amount of adsorbed NH3 species on the Bronsted acid site and CB/CL, it suppressed the production of N2O by inhibiting the production of NH species, the deep dehydrogenation of ammonia adsorption species. This study provided a simple design strategy for the catalyst to improve the low-temperature catalytic performance and N2 selectivity.

Ethane Dehydrogenation over the Core–Shell Pt-Based Alloy Catalysts: Driven by Engineering the Shell Composition and Thickness

Pt-based catalysts as the commercial catalysts in ethane dehydrogenation (EDH) face one of the main challenges of realizing the balance between coke formation and catalytic activity. In this work, a strategy to drive the catalytic performance of EDH on Pt-Sn alloy catalysts is proposed by rationally engineering the shell surface structure and thickness of core-shell Pt@Pt3Sn and Pt3Sn@Pt catalysts from a theoretical perspective. Eight types of Pt@Pt3Sn and Pt3Sn@Pt catalysts with different Pt and Pt3Sn shell thicknesses are considered and compared with the industrially used Pt and Pt3Sn catalysts. Density functional theory (DFT) calculations completely describe the reaction network of EDH, including the side reactions of deep dehydrogenation and C-C bond cracking. Kinetic Monte Carlo (kMC) simulations reveal the influences of the catalyst surface structure, experimentally related temperatures, and reactant partial pressures. The results show that CHCH* is the main precursor for coke formation, and Pt@Pt3Sn catalysts generally have higher C2H4(g) activity and lower selectivity compared to those of Pt3Sn@Pt catalysts, which is attributed to the unique surface geometrical and electronic properties. 1Pt3Sn@4Pt and 1Pt@4Pt3Sn are screened out as catalysts exhibiting excellent performance; especially, the 1Pt3Sn@4Pt catalyst has much higher C2H4(g) activity and 100% C2H4(g) selectivity compared to those of 1Pt@4Pt3Sn and the widely used Pt and Pt3Sn catalysts. The two descriptors C2H5* adsorption energy and reaction energy of its dehydrogenation to C2H4* are proposed to qualitatively evaluate the C2H4(g) selectivity and activity, respectively. This work facilitates a valuable exploration for optimizing the catalytic performance of core-shell Pt-based catalysts in EDH and reveals the great importance of the fine control of the catalyst shell surface structure and thickness.

Nonoxidative Coupling of Methane to Produce C2 Hydrocarbons on FLPs of an Albite Surface.

The characteristics of active sites on the surface of albite were theoretically analyzed by density functional theory, and the activation of the C-H bond of methane using an albite catalyst and the reaction mechanism of preparing C2 hydrocarbons by nonoxidative coupling were studied. There are two frustrated Lewis pairs (FLPs) on the (001) and (010) surfaces of albite; they can dissociate H2 under mild conditions and show high activity for the activation of methane C-H bonds. CH4 molecules can undergo direct dissociative adsorption on the (010) surface, whereas a 50.07 kJ/mol activation barrier is needed on the (001) surface. The prepared albite catalyst has a double combination function of the (001) and (010) surfaces; these surfaces produce a spillover phenomenon in the process of CH4 activation reactions, where CH3 overflows from the (001) surface with CH3 adsorbed on the (010) surface to achieve nonoxidative high efficiently C-C coupling with an activation energy of 18.51 kJ/mol. At the same time, this spillover phenomenon inhibits deep dehydrogenation, which is conducive to the selectivity of the C2 hydrocarbons. The experimental results confirm that the selectivity of the C2 hydrocarbons is maintained above 99% in the temperature range of 873 K to 1173 K.

Unveiling the origin of enhanced catalytic performance of NiCu alloy for semi-hydrogenation of acetylene

Ni-based bimetallic catalysts are widely explored for semi-hydrogenation of acetylene due to their enhanced catalytic performance. However, the comprehensive understanding of performance promoted by Ni-based alloy still remains elusive to date. Herein, supported NiCu/ZrO2 catalysts were fabricated to unveil the origin of improved selectivity and stability. Owing to the electronic and geometric modification of active Ni sites by Cu atoms, NiCu/ZrO2 ensures weak adsorption of key intermediates and easy desorption of ethylene, leading to an improved selectivity towards ethylene. DFT calculations indicate that both the activation barriers for the acetylene deep dehydrogenation pathway and the CC bond cleavage pathway on NiCu alloy are higher, suggesting that NiCu/ZrO2 would show superior stability over Ni/ZrO2. Therefore, the ID/IG ratio obtained via in-situ Raman, which represents the anti-coking ability of catalysts, can be employed as a descriptor of catalytic stability. These findings bring new insight for designing efficient heterogeneous catalysts for selective hydrogenation.

Insights and Activation Energy Surface of the Dehydrogenation of C2 Hx O Species in Ethanol Oxidation Reaction on Ir(100).

Dehydrogenation of an organic compound is the first and the most fundamental elementary reaction in many organic reactions. In ethanol oxidation reaction (EOR) to form CO2 , there are a total of 46 pathways in C2 Hx O (x=1-6) species leading to the removal of all six hydrogen atoms in five C-H bonds and one O-H bond. To investigate the degree of dehydrogenation in EOR under operando conditions, we performed density function theory (DFT) calculations to study 28 dehydrogenation steps of C2 Hx O on Ir(100). An activation energy surface was then constructed and compared with that of the C-C bond cleavages to understand the importance of the degree of dehydrogenation in EOR. The results show that there are likely 28 dehydrogenations in EOR under fuel cell temperatures and the last two hydrogens in C2 H2 O are less likely cleaved. On the other hand, deep dehydrogenation including 45 dehydrogenations can occur under ethanol steam reforming conditions.

Size-Dependent Microwave Heating and Catalytic Activity of Fine Iron Particles in the Deep Dehydrogenation of Hexadecane.

Knowledge of the electromagnetic microwave radiation–solid matter interaction and ensuing mechanisms at active catalytic sites will enable a deeper understanding of microwave-initiated chemical interactions and processes, and will lead to further optimization of this class of heterogeneous catalysis. Here, we study the fundamental mechanism of the interaction between microwave radiation and solid Fe catalysts and the deep dehydrogenation of a model hydrocarbon, hexadecane. We find that the size-dependent electronic transition of particulate Fe metal from a microwave “reflector” to a microwave “absorber” lies at the heart of efficient metal catalysis in these heterogeneous processes. In this regard, the optimal particle size of a Fe metal catalyst for highly effective microwave-initiated dehydrogenation reactions is approximately 80–120 nm, and the catalytic performance is strongly dependent on the ratio of the mean radius of Fe particles to the microwave skin depth (r/δ) at the operating frequency. Importantly, the particle size of selected Fe catalysts will ultimately affect the basic heating properties of the catalysts and decisively influence their catalytic performance under microwave initiation. In addition, we have found that when two or more materials—present as a mechanical mixture—are simultaneously exposed to microwave irradiation, each constituent material will respond to the microwaves independently. Thus, the interaction between the two materials has been found to have synergistic effects, subsequently contributing to heating and improving the overall catalytic performance.

The structural decoration of Ru catalysts by boron for enhanced propane dehydrogenation

Propane dehydrogenation (PDH) is an efficient technology for the direct production of propylene. Nevertheless, current PDH catalysts mainly rely on precious Pt or toxic Cr and especially undergo severe coke deposition. Herein, we report a Ru catalyst decorated by boron species (Ru-3B/Al2O3), which exhibits high catalytic performance for PDH. HAADF-STEM, EELS, and CO-FTIR characterization are used to identify the surface structure of the Ru active component, which shows that the high-energy unsaturated coordination sites, including corners, edges and step atoms for Ru-3B/Al2O3, are appropriately modified by BOx species. The encapsulation of high-energy active sites prone to CC cracking and deep dehydrogenation leads to higher propylene selectivity (> 95%) and strong carbon resistance (kd 0.0007 min) over Ru-3B/Al2O3. The XPS and H2-TPR results show that the migration of B species is driven by the reduction of B2O3 to B2O2 and that the coating degree of Ru particles is controlled by the chemical valance of Ru species.

Framework Zr Stabilized PtSn/Zr‐MCM‐41 as a Promising Catalyst for Non‐oxidative Ethane Dehydrogenation

Comprehensive SummaryNon‐oxidative ethane dehydrogenation is a promising route to produce ethene. Herein, PtSn supported catalysts were investigated to achieve better ethane dehydrogenation performance by introduction of different Zr promoters, i.e., framework Zr and ZrO2, to mesoporous MCM‐41. In‐situ XRD, TEM and CO chemisorption show that aggregation of metal particles and phase segregation of Pt3Sn to Pt and PtSn3 at high temperature occur for PtSn/M, leading to bad ethane dehydrogenation activity. Strong interaction between ZrO2 and PtSn species, as proved by XPS, results in restrained metal particles, which promotes the initial reactivity. However, Pt phase generated on surface is disadvantageous for the desorption of produced ethene as indicated by CO‐IR and C3H6‐TPD, and pyridine‐IR and NH3‐TPD indicate strong acidity generated. Both deactivate the catalyst rapidly by deep dehydrogenation and coking. Moderate interaction between PtSn species and Si‐O‐Zr with much weaker acidity is formed when framework Zr is incorporated into MCM‐41, which benefits the dispersion of metal particles, formation of Pt3Sn/Pt species and stabilization of metal species from phase segregation. Outstanding initial ethane conversion and ethene selectivity of ca. 99% were achieved for the optimal PtSn/ZrM, which is more coking‐tolerant and stable by generating graphitic carbon mainly on support instead of active metals.

Nonoxidative Coupling of Methane over Ceria-Supported Single-Atom Pt Catalysts in DBD Plasma.

Plasma-catalytic direct nonoxidative coupling of methane (NCM) into C2 hydrocarbons was investigated over ceria-supported atomically dispersed Pt (Pt/CeO2-SAC) and nanoparticle Pt (Pt/CeO2-NP) catalysts in dielectric barrier discharge (DBD) plasma. Nonthermal plasma facilitated C-H bond dissociation in CH4 at low temperatures (<150 °C) and atmospheric pressure. The presence of Pt/CeO2 catalysts in plasma further enhanced CH4 conversion and C2 hydrocarbon selectivity by enabling the conversion of vibrationally excited methane species with high internal energy on active Pt sites. Noticeably, the Pt/CeO2-SAC catalyst displayed a more remarkable performance, with a CH4 conversion of 39% and a C2 selectivity of 54% at 54 W. The enhanced CH4 conversion was attributed to abundant coordinatively unsaturated Pt sites in Pt/CeO2-SAC, which were more active for C-H bond scission. Meanwhile, isolated Pt atoms in Pt/CeO2-SAC promoted C2 hydrocarbon formation by hindering the unselective formation of coke from deep dehydrogenation of CHx• intermediates and higher hydrocarbons from oligomerization reactions.